Semiconductor device including non-volatile memory cells

ABSTRACT

A semiconductor device includes a non-volatile memory (NVM) cell. The NVM cell includes a semiconductor wire disposed over an insulating layer disposed on a substrate. The NVM cell includes a select transistor and a control transistor. The select transistor includes a gate dielectric layer disposed around the semiconductor wire and a select gate electrode disposed on the gate dielectric layer. The control transistor includes a stacked dielectric layer disposed around the semiconductor wire and a control gate electrode disposed on the stacked dielectric layer. The stacked dielectric layer includes a charge trapping layer. The select gate electrode is disposed adjacent to the control gate electrode with the stacked dielectric layer interposed therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/201,358 filed Nov. 27, 2018, which is a divisional application ofU.S. patent application Ser. No. 15/644,506, filed on Jul. 7, 2017, nowU.S. Pat. No. 10,276,728, the entire disclosures of each of which areincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to method of manufacturing semiconductorintegrated circuits, and more particularly to a semiconductor deviceincluding a non-volatile memory and a method of manufacturing the same.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs. Integration ofa non-volatile memory in a semiconductor device has achieved a higherfunctionality of the semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a perspective view of a non-volatile memory cell inaccordance with embodiments of the present disclosure. FIG. 1B is across sectional view corresponding to the plane P_(XY) along X1-X1 lineof FIG. 1A, FIG. 1C is a cross sectional view corresponding to lineY2-Y2 of FIG. 1A and FIG. 1D is a cross sectional view corresponding toline Y1-Y1 of FIG. 1A. FIG. 1E is a perspective view of a non-volatilememory array in accordance with embodiments of the present disclosure.

FIG. 2 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 3 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 4 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 5 illustrates one of the various stages in a semiconductor devicefabrication process with a cross sectional view in accordance withembodiments of the present disclosure.

FIG. 6 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 7 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 8 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 9 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 10 illustrates one of the various stages in a semiconductor devicefabrication process with an enlarged view in accordance with embodimentsof the present disclosure.

FIG. 11 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 12 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 13 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 14 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 15 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 16 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure.

FIG. 17 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 18 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 19 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 20 illustrates one of the various stages in a semiconductor devicefabrication process with a cross sectional view in accordance with otherembodiments of the present disclosure.

FIG. 21 illustrates one of the various stages in a semiconductor devicefabrication process with a cross sectional view in accordance with otherembodiments of the present disclosure.

FIG. 22A illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure. FIG. 22B is a cross sectional view corresponding to lineY2-Y2 of FIG. 22A and FIG. 22C is a cross sectional view correspondingto line Y1-Y1 of FIG. 22A.

FIG. 23 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 24 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 25 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

FIG. 26 illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity. In the accompanied drawings, some layers/features may beomitted for simplification.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.” Further, inthe following fabrication process, there may be one or more additionaloperations in/between the described operations, and the order ofoperations may be changed.

In some embodiments, a semiconductor device includes non-volatile memory(NVM) cells, such as a semiconductor-oxide-nitride-oxide-semiconductor(SONOS) type NVM cell. In particular, the present embodiments aredirected to a 1.5-transistor (1.5 T) SONOS NVM cell utilizing agate-all-around structure.

FIGS. 1A-1D illustrate a structure of a 1.5 T SONOS NVM cell inaccordance with some embodiments of the present disclosure. FIG. 1B is across sectional view corresponding to the plane P_(XY) along X1-X1 lineof FIG. 1A, FIG. 1C is a cross sectional view corresponding to lineY2-Y2 of FIG. 1A and FIG. 1D is a cross sectional view corresponding toline Y1-Y1 of FIG. 1A.

As shown in FIGS. 1A-1D, the 1.5 T SONOS NVM cell includes two pairs ofa control transistor CG and a select transistor SG, both of which areGAA FETs. These transistors are disposed over an insulating layer 20disposed on a substrate 10. Since two memory cells shares one drain, thedevice of FIGS. 1A-1D is a 1.5 T NVM device.

The select transistor SG includes a semiconductor wire 35 extending inthe X direction, a gate dielectric layer 130 wrapping around a part ofthe semiconductor wire (channel) 35C1 or 35C2, and a select gate (SG)electrode 70S formed on the gate dielectric layer 130 wrapping aroundthe part of the semiconductor wire 35C1 or 35C2. In some embodiments,the gate dielectric layer 130 is also disposed on the insulating layer20.

The pairs of the control transistor CG and the select transistor SGshare a drain 35D, which is a part of the semiconductor wire 35, andhave sources 35S1 and 35S2, which are also a part of the semiconductorwire 35. In the present disclosure, the terms “a source” and “a drain”may be used to distinguish one from the other, and may beinterchangeably used.

The control transistor CG includes a semiconductor wire 35, a stackeddielectric layer 120 wrapping around a part of the semiconductor wire(channel) 35C1 or 35C2, and a control gate (CG) electrode 70C formed onand around the stacked gate dielectric layer 120 wrapping around thepart of the semiconductor wire 35C1 or 35C2. In some embodiments, thestacked dielectric layer 120 is disposed between the CG electrode 70Cand the SG electrode 70S and is also disposed on the insulating layer20.

The semiconductor wire 35 is formed as one wire structure and hascorresponding anchor portions 30. The semiconductor wire 35 is made of asuitable semiconductor, such as silicon or germanium; a suitable alloyor compound semiconductor, such as Group-IV compound semiconductors(silicon germanium (SiGe), silicon carbide (SiC), silicon germaniumcarbide (SiGeC), GeSn, SiSn, SiGeSn), Group III-V compoundsemiconductors (e.g., gallium arsenide, indium gallium arsenide InGaAs,indium arsenide, indium phosphide, indium antimonide, gallium arsenicphosphide, or gallium indium phosphide), or the like. The semiconductorwire 35 is appropriately doped with impurities. The thickness T1, T2 ofsemiconductor wire 35 in the select transistor SG and the controltransistor CG is in a range from about 3 nm to 25 nm, and the width W1,W2 of semiconductor wire 35 is in a range from about 3 nm to 10 nm, insome embodiments. The cross sectional shape of the semiconductor wire 35may be substantially square with rounded corners, rectangular withrounded corners, triangular with rounded corners, polygonal with roundedcorners, oval, circular, or the like.

In some embodiments, the gate dielectric layer 130 is made of SiO₂formed by chemical vapor deposition (CVD) or atomic layer deposition(ALD). In other embodiments, the gate dielectric layer 130 includes oneor more high-k dielectric layers having a dielectric constant greaterthan that of SiO₂. For example, the gate dielectric layer 130 mayinclude one or more layers of a metal oxide or a silicate of Hf, Al, Zr,combinations thereof, and multi-layers thereof. Other suitable materialsinclude La, Mg, Ba, Ti, Pb, Zr, in the form of metal oxides, metal alloyoxides, and combinations thereof. Exemplary materials include MgO_(x),BaTi_(x)O_(y), BaSr_(x)Ti_(y)O_(z), PbTi_(x)O_(y), PbZr_(x)Ti_(y)O_(z),SiCN, SiON, SiN, Al₂O₃, La₂O₃, Ta₂O₃, Y₂O₃, HfO₂, ZrO₂, HfSiON,YGe_(x)O_(y), YSi_(x)O_(y) and LaAlO₃, and the like. In someembodiments, the gate dielectric layer 130 has a thickness T3 of about 1nm to about 8 nm.

The stacked dielectric layer 120 includes a first dielectric layer 121disposed on and around the semiconductor wire 35, a second dielectriclayer 122 disposed on the first dielectric layer 121 and a thirddielectric layer 123 disposed on the second dielectric layer. As shownin FIG. 1D, the stacked dielectric layer 120 is also disposed on theinsulating layer 20. In some embodiments, the first and third dielectriclayers 121 and 123 are made of SiO₂ or other suitable metal oxidedielectric materials. The stacked dielectric layer 120 has a thicknessT4 of about 5 nm to about 25 nm in some embodiments. In someembodiments, the first dielectric layer has a thickness of about 1 nm toabout 5 nm the third dielectric layer has a thickness of about 2 nm toabout 8 nm. The second dielectric layer 122, which functions as a chargetrapping layer of an NVM cell, is made of one or more of SiN, SiON,HfO₂, ZrO₂ or other suitable dielectric materials in some embodiments.Si-dots may be used as the charge trapping layer in certain embodiments.In some embodiments, second dielectric layer 122 has a thickness ofabout 2 nm to about 12 nm.

The gate electrodes 70S and 70C include one or more conductivematerials, such as W, Cu, Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn,Co, Pd, Ni, Re, Jr, Ru, Pt, and/or Zr, or any other suitable material.In some embodiments, the gate electrodes 70S and 70C include aconductive material, such as TiN, WN, TaN, and/or Ru. Metal alloys suchas Ti—Al, Ru—Ta, Ru—Zr, Pt—Ti, Co—Ni and Ni—Ta may be used and/or metalnitrides such as WN_(x), TiNX, MoN_(x), TaN_(x), and TaSi_(x)N_(y) maybe used. In certain embodiments of the present disclosure, the gateelectrodes 70S and 70C include one or more work function adjustmentlayers disposed on the gate dielectric layer 130. The work functionadjustment layer is made of a conductive material such as a single layerof TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi or TiAlC,or a multilayer of two or more of these materials, or any other suitablematerial. For the n-channel FinFET, one or more of TaN, TaAlC, TiN, TiC,Co, TiAl, HfTi, TiSi and TaSi, or any other suitable material is used asthe work function adjustment layer, and for the p-channel FinFET, one ormore of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC and Co, or any othersuitable material is used as the work function adjustment layer.

The width L1 of the select gate electrode 70S is in a range from about 5nm to about 50 nm and the width L2 of the select gate electrode 70C isin a range from about 5 nm to about 50 nm, in some embodiments. Thewidth L1 may be the same as or different from the width L2. A space S1between the end of one select gate electrode and the end of the otherselect gate electrode is in a range from about 30 nm to about 200 nm,and a space S2 between the end of the control gate electrode and theanchor portion is in a range from about 30 nm to about 200 nm, in someembodiments. In some embodiments, one or more sidewall spacers (notshown) are disposed on one side of the select gate electrode 70S and oneside of the control gate electrode 70C. The height H1 of the controlgate electrode 70C is smaller than the height H2 of the select gateelectrode 70S in some embodiments. The height H1 of the control gateelectrode 70C is greater than the height H2 of the select gate electrode70S in other embodiments.

In some embodiments, the substrate 10 may be made of a suitablesemiconductor, such as silicon, diamond or germanium; a suitable alloyor compound semiconductor, such as Group-IV compound semiconductors(silicon germanium (SiGe), silicon carbide (SiC), silicon germaniumcarbide (SiGeC), GeSn, SiSn, SiGeSn), Group III-V compoundsemiconductors (e.g., gallium arsenide, indium gallium arsenide InGaAs,indium arsenide, indium phosphide, indium antimonide, gallium arsenicphosphide, or gallium indium phosphide), or any other suitable material.The insulating layer 20 may be made of SiO₂ or other suitable insulatingmaterial.

FIG. 1E is a perspective view of a non-volatile memory cell array inaccordance with embodiments of the present disclosure. In FIG. 1E, twoor more semiconductor wires are disposed over the substrate and theselect gate electrodes and the control gate electrodes are disposed overthe two or more semiconductor wires. The drains are coupled to bit linesand select gate electrodes and control gate electrodes function as wordlines. The sources may be coupled to appropriate power supplies.

FIGS. 2-16 illustrate various stages of a semiconductor devicefabrication process in accordance with embodiments of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 2-16, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable.

In FIG. 2, a semiconductor-insulator-semiconductor structure including asubstrate 10, an insulating layer 20 and an upper semiconductor layer 28is prepared. In some embodiments, thesemiconductor-insulator-semiconductor structure is asilicon-on-insulator (SOI) wafer. The thickness of the insulating layer20 is in a range from about 100 nm to 3000 nm in some embodiments. Thethickness of the upper semiconductor layer 28 is in a range from about10 nm to 200 nm in some embodiments.

As shown in FIG. 3, impurities are introduced into the uppersemiconductor layer 28, thereby forming a doped upper semiconductorlayer 29. The impurities, such as P, As, In, B and/or BF₂, areintroduced by one or more ion implantation operations with appropriatephoto lithography operations. The doping concentration for the dopedupper semiconductor layer 29 is in a range from about 10×10¹² to about10×10¹⁵ cm⁻³ in some embodiments. In some embodiments, the implantationoperation(s) is not performed at this stage of the manufacturingoperation, but rather is performed at a later stage.

Then, as shown in FIG. 4, a mask pattern 40 is formed over the dopedupper semiconductor layer 29. The mask pattern 40 may be a photo resistpattern or a hard mask pattern formed by one or more layers of SiO₂ andSiN, or any other suitable material. The mask pattern 40 may have an “I”shape having a main portion and anchor portions disposed at both ends ofthe main portion.

Next, as shown in FIG. 5, which also shows a cross sectional view, thedoped upper semiconductor layer 29 is patterned by using the maskpattern 40 as an etching mask, and the insulating layer 20 is recessedby dry and/or wet etching. By this recess etching, the insulating layer20 under the main portion of the “I” shape of the upper semiconductorlayer 29 is removed, thereby forming a semiconductor wire 35, and anchorportions 30, as shown in FIG. 5. In some embodiments, the implantationoperation(s) for the doped upper semiconductor is performed after thewire structure 35 is formed. Subsequently, the mask pattern 40 isremoved.

After the semiconductor wire is formed, a gate dielectric layer 130 isformed around the semiconductor wire 35 and on other portions includingthe upper surface of the recessed insulating layer 20, as shown in FIG.6. The gate dielectric layer 130 can be formed by thermal oxidation,chemical vapor deposition (CVD), physical vapor deposition (PVD) oratomic layer deposition (ALD).

Subsequently, as shown in FIG. 7, a first gate layer 70 is formed overthe gate dielectric layer 130 by CVD, PVD or ALD or any other suitablemethods. The first gate layer 70 may be doped polysilicon or dopedamorphous silicon. The first gate layer 70 is formed on the gatedielectric layer 130 wrapping around the semiconductor wire 35 and onthe gate dielectric layer 130 formed at the other portions. Thesemiconductor wire 35 with the gate dielectric layer 130 is fullyembedded in the first gate layer 70.

Then, as shown in FIG. 8, a mask pattern 42 is formed over the firstgate layer 70. By using a dry etching operation, the first gate layer 70is patterned into select gate electrodes 70S. As shown in FIG. 9, thegate dielectric layer 130 is further etched, except for the region underthe select gate electrodes, by using suitable etching gas. After theselect gate electrodes 70S are formed by etching, the semiconductor wire35 is exposed except for the portions covered by the select gateelectrodes 70S.

In certain embodiments, the mask pattern 42 is a photo resist pattern,and by using the photo resist pattern, the first gate layer 70 isetched. In other embodiments, a hard mask layer made of one or morelayers of SiO₂ and SiN is formed on the first gate layer 70, and thehard mask layer is patterned by etching using the resist mask pattern42. Further, the first gate layer 70 is patterned by using the patternedhard layer.

After the select gate electrode 70S are formed, a stacked dielectriclayer 120 is formed. The stacked layer 120 includes a first portionformed on and around the exposed semiconductor wire 35 and a secondportion formed on the other remaining portions including the select gateelectrodes 70S and over the substrate, as shown in FIG. 10. The stackeddielectric layer 120 including the first to third dielectric layers 121,122, 123 can be formed by thermal oxidation, chemical vapor deposition(CVD), physical vapor deposition (PVD) or atomic layer deposition (ALD).

Then, as shown in FIG. 11, a second gate layer 95 is formed over thestacked dielectric layer 120. The second gate layer 70 may be dopedpolysilicon or doped amorphous silicon. Then, as shown in FIG. 12, anetch-back operation using dry etching is performed to expose the upperportions of the stacked dielectric layer 120 formed on the select gateelectrodes 70S and formed on the semiconductor wire 35. By the etch-backoperation, sidewall structures 96, 97 are formed on opposing side facesof the select gate electrode 70 covered with stacked dielectric layer120.

Further, as shown FIG. 13, a mask pattern 44 is formed over thestructure of FIG. 12. The mask pattern 44 is a resist pattern in someembodiments. The mask pattern 44 covers the sidewall structures 96.Then, by using dry and/or wet etching, the second gate layers 95 notcovered by the mask pattern 44 are removed, thereby forming control gateelectrodes 70C.

Next, as shown in FIG. 15, the third dielectric layer 123 and the seconddielectric layer 122 are removed by dry and/or wet etching. Accordingly,the first dielectric layer 121 remains on the anchor portions 30, theinsulating layer 20 and the upper surface of the select gate electrode,as shown in FIG. 15. In some embodiments, the third dielectric layer 123and the second dielectric layer 122 are not removed, or only the thirddielectric layer 123 is removed.

Subsequently, as shown in FIG. 16, one or more ion implantationoperations with or without a resist mask are performed to introducedopant to the source regions 35S1, 35S2 and the drain region 35D of thesemiconductor wire covered by the stacked dielectric layer 120. Theimpurities are, for example, Ge, C, P, As, In, B and/or BF₂ in someembodiments. The doping concentration is in a range from about 10×10¹²to about 10×10¹⁵ cm⁻³ in some embodiments.

As shown in FIG. 16, the control gate electrode and the select gateelectrode are adjacent to each other with only the stacked dielectriclayer 120 (the second portion of the stacked dielectric layer)interposed therebetween (no other layer exits). Further, a part of thegate dielectric layer 130 is disposed between the select gate electrode70S and the insulating layer 20, and a part of the stacked dielectriclayer 120 (a third portion of the stacked dielectric layer) is disposedbetween the control gate electrode 70C and the insulating layer 20. Nogate dielectric layer is interposed between the control gate 70C and thestacked dielectric layer 120 in some embodiments.

In some embodiments, before and/or after the ion implantation, one ormore sets of sidewall spacers are formed on one side face of the controlgate electrode 70C not facing the select gate electrode 70S and on oneside face of the select gate covered with the first dielectric layer 121not facing the control gate electrode 70C. The sidewall spacers mayinclude one or more layers of SiO₂, SiN, SiON, SiOCN or other suitabledielectric materials and may be formed by depositing a film andanisotropic etching. The thickness of the sidewall spacers is in a rangefrom about 5 nm to about 50 nm in some embodiments. Further, in someembodiments, a bottom-contact-etch-stop layer (BESL) formed over thestructure of FIG. 16, and further, one or more interlayer dielectric(ILD) layers is formed on the BESL. The thickness of the BESL is in arange from about 5 nm to about 30 nm in some embodiments.

After the structure of FIG. 16 is formed, further CMOS processes areperformed to form various features such as additional interlayerdielectric layers, contacts/vias, interconnect metal layers, andpassivation layers, etc.

FIGS. 17-21 illustrate various stages of a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 17-21, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. Materials, configurations,processes and/or operations the same as or similar to those explainedwith respect to FIGS. 1A-16 may be applied to the following embodiments,and the detailed explanation thereof may be omitted to avoid redundancy.

As show in FIG. 17, a substrate (e.g., a Si wafer) 10′ is prepared. Thesubstrate 10′ may be made of Ge, Group-IV compound semiconductors orGroup III-V compound semiconductors, or any other suitable material inother embodiments. Then, similar to the operations of FIG. 3, impuritiesare introduced into the upper portion of the substrate 10′, therebyforming a doped layer 29′, as shown in FIG. 18. Similar to FIG. 4, amask pattern 40 is formed over the doped layer 29′, as shown in FIG. 19.

Then, the doped layer 29′ and the substrate 10′ are etched to form thesemiconductor wire 35′ and anchor portions 30′, as shown in FIG. 20,which also shows a cross sectional view. To form the semiconductor wire,a combination of anisotropic and isotropic etching is used. In theanisotropic etching, a combination of an isotropic etching operation ofsilicon using SF₆ and a sidewall passivation step using C₄F₈ isutilized. These two steps are repeated to form a vertical recess,followed by the isotropic etching using SF₆. Since the etching using SF₆proceeds along the lateral direction as well as the vertical direction,a portion of the substrate 10′ under the mask pattern (under thesemiconductor wire to be formed) is removed, thereby releasing thesemiconductor wire from the substrate 10′. In some embodiments, aprotrusion 19 may be formed under the semiconductor wire 35′, as shownin FIG. 20.

Subsequently, an insulating layer 20′ is formed in the recessedsubstrate 10′, as shown in FIG. 21. The insulating layer 20′ may be madeof suitable dielectric materials such as silicon oxide, silicon nitride,silicon oxynitride, fluorine-doped silicate glass (FSG), low-kdielectrics such as carbon doped oxides, extremely low-k dielectricssuch as porous carbon doped silicon dioxide, a polymer such aspolyimide, combinations of these, or the like. In some embodiments, theinsulating layer 20′ is formed through a process such as CVD, flowableCVD (FCVD), or a spin-on-glass process, although any acceptable processmay be utilized. Subsequently, unnecessary portions of the insulatinglayer 20′ are removed using, for example, an etch process, chemicalmechanical polishing (CMP), or the like. After the layer 20′ is formed,the operations for forming the NVM cell structure as explained withFIGS. 6-16 are performed.

FIG. 22A illustrates one of the various stages in a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure. FIG. 22B is a cross sectional view corresponding to lineY2-Y2 of FIG. 22A and FIG. 22C is a cross sectional view correspondingto line Y1-Y1 of FIG. 22A. The structure of FIGS. 22A-22C issubstantially the same as the structure of FIGS. 1A-1D except that theprotrusion 19 is formed under the semiconductor wire 35′ and embedded inthe insulating layer 20′, as shown in FIG. 20.

FIGS. 23-26 illustrate various stages of a semiconductor devicefabrication process in accordance with other embodiments of the presentdisclosure. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 23-26, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. Materials, configurations,processes and/or operations same as or similar to those explained withrespect to FIGS. 1A-22 may be applied to the following embodiments, andthe detailed explanation thereof may be omitted to avoid redundancy.

As shown in FIG. 23, a first semiconductor layer 11 is epitaxiallyformed on a substrate 10″ and a second semiconductor layer 12 isepitaxially formed on the first semiconductor layer 11. In someembodiments, the substrate 10″ is Si, the first semiconductor layer 11is made of SiGe, and the second semiconductor layer 12 is made of Si.

Then, similar to the operations of FIG. 3, impurities are introduced inthe second semiconductor layer 12, thereby forming a doped secondsemiconductor layer 29″, as shown in FIG. 24. Similar to FIG. 4, a maskpattern 40 is formed over the doped second semiconductor layer 29″, asshown in FIG. 25.

Then, the doped second semiconductor layer 29″ and the substrate 10″ areetched to form the semiconductor wire 35″ and anchor portions 30″, asshown in FIG. 26. To form the semiconductor wire, the secondsemiconductor layer 12 is etched by using the mask pattern 40 as anetching mask, and then part of the first semiconductor layer 11 isremoved. The first semiconductor layer 11 may be selectively removedusing a wet etchant such as, but not limited to, ammonium hydroxide(NH₄OH), tetramethylammonium hydroxide (TMAH), ethylenediaminepyrocatechol (EDP), or potassium hydroxide (KOH) solution. Subsequently,the mask pattern 40 is removed.

In some embodiments, a protrusion similar to that shown in FIG. 20 maybe formed under the semiconductor wire 35″.

Subsequently, similar to FIG. 11, an insulating layer is formed in therecessed first semiconductor layer 11. In some embodiments, the firstsemiconductor layer under the semiconductor wire 35″ is fully removed toexpose the substrate 10″. After the insulating layer is formed, theoperations for forming the NVM cell structure as explained with FIGS.6-16 are performed.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

For example, in the present disclosure, a 1.5 T-SONOS NVM cell having aselect transistor and a control transistor is employed, which is easierto be scaled down compared with a NVM cell having a floating gate.Further, by employing a gate-all-around structure, it is possible tomore precisely control the memory operation and to improvewrite/read/erase operations. In addition, it is possible to furtherreduce the device size.

In accordance with an aspect of the present disclosure, in a method offorming a semiconductor device including a non-volatile memory (NVM)cell, a semiconductor wire is formed over an insulating layer disposedon a substrate. A gate dielectric layer is formed wrapped around thesemiconductor wire. A select gate electrode is formed around thesemiconductor wire wrapped by the gate dielectric layer. A first stackeddielectric layer is formed around the semiconductor wire not covered bythe select gate electrode and a second stacked dielectric layer isformed on the select gate electrode. A control gate electrode is formedaround the semiconductor wire wrapped by the first stacked dielectriclayer and adjacent to one face of the select gate electrode with thesecond stacked dielectric layer interposed therebetween. In one or moreforegoing or following embodiments, the semiconductor wire is formed byforming a mask pattern on a semiconductor layer disposed on theinsulating layer, patterning the semiconductor layer by using the maskpattern as an etching mask, and removing part of the insulating layer,thereby forming the semiconductor wire. In one or more foregoing orfollowing embodiments, before forming the mask pattern, a doped layer isformed in the semiconductor layer by one or more ion implantationoperations. In one or more foregoing or following embodiments, after thesemiconductor wire is formed, one or more ion implantation operationsare performed, thereby introducing impurities into the semiconductorwire. In one or more foregoing or following embodiments, thesemiconductor wire is formed by forming a mask pattern on the substrate,etching the substrate, thereby forming a recess in the substrate and thesemiconductor wire disposed over the recess, and forming the insulatinglayer in the recess. In one or more foregoing or following embodiments,before forming the mask pattern, a doped layer is formed in thesubstrate by one or more ion implantation operations. In one or moreforegoing or following embodiments, after the semiconductor wire isformed, one or more ion implantation operations are performed, therebyintroducing impurities into the semiconductor wire. In one or moreforegoing or following embodiments, the first and second stackeddielectric layers include a first dielectric layer disposed on thecontrol gate portion of the semiconductor wire, a second dielectriclayer disposed on the first dielectric layer, and a third dielectriclayer disposed on the second dielectric layer. In one or more foregoingor following embodiments, the second dielectric layer includes one ormore materials selected from the group consisting of SiN, SiON, HfO₂,ZrO₂ and Si-dots. In one or more foregoing or following embodiments,after the control gate electrode is formed, the first stacked dielectriclayer which is not covered by the select gate is removed.

In accordance with another aspect of the present disclosure, asemiconductor device including a non-volatile memory (NVM) cell. The NVMcell includes a semiconductor wire disposed over an insulating layerdisposed on a substrate. The NVM cell includes a select transistor and acontrol transistor. The select transistor includes a gate dielectriclayer disposed around the semiconductor wire and a select gate electrodedisposed on the gate dielectric layer. The control transistor includes afirst stacked dielectric layer disposed around the semiconductor wireand a control gate electrode disposed on the first stacked dielectriclayer. The select gate electrode is disposed adjacent to the controlgate electrode with a second stacked dielectric layer interposedtherebetween. The first and second stacked dielectric layers include acharge trapping layer. In one or more foregoing or followingembodiments, the first and second stacked dielectric layers furtherinclude a first dielectric layer made of oxide and a third dielectriclayer made of oxide and disposed on the charge trapping layer, and thecharge trapping layer is disposed on the first dielectric layer. In oneor more foregoing or following embodiments, the charge trapping layerincludes one or more materials selected from the group consisting ofSiN, SiON, HfO₂, ZrO₂ and Si-dots. In one or more foregoing or followingembodiments, a part of the gate dielectric layer is disposed between theselect gate electrode and the insulating layer. In one or more foregoingor following embodiments, a part of the second stacked dielectric layeris disposed between the control gate electrode and the insulating layer.In one or more foregoing or following embodiments, a height of thecontrol gate electrode is greater than a height of the select gateelectrode.

In accordance with another aspect of the present disclosure, asemiconductor device includes a non-volatile memory (NVM) cell. The NVMcell includes a semiconductor wire disposed over an insulating layerdisposed on a substrate. The NVM cell includes a first controltransistor, a select transistor, a second select transistor and a secondcontrol transistor, which are arranged in this order along an extendingdirection of the semiconductor wire. The first and second selecttransistors include a gate dielectric layer disposed around thesemiconductor wire and a select gate electrode disposed on the gatedielectric layer. The first and second control transistors include afirst stacked dielectric layer disposed around the semiconductor wireand a control gate electrode disposed on the stacked dielectric layer.The first select gate electrode is disposed adjacent to the firstcontrol gate electrode with a second stacked dielectric layer interposedtherebetween, and the second select gate electrode is disposed adjacentto the second control gate electrode with a third stacked dielectriclayer interposed therebetween. The first to third stacked dielectriclayers include a charge trapping layer. The semiconductor wire includesa shared drain portion disposed between the select gate electrode of thefirst select transistor and the select gate electrode of the secondselect transistor. In one or more foregoing or following embodiments,the first and second stacked dielectric layers further include a firstdielectric layer made of an oxide and a third dielectric layer made ofan oxide and disposed on the charge trapping layer, the charge trappinglayer is disposed on the first dielectric layer, and the charge trappinglayer includes one or more materials selected from the group consistingof SiN, SiON, HfO₂ and ZrO₂. In one or more foregoing or followingembodiments, a part of the gate dielectric layer is disposed between theselect gate electrode and the insulating layer, and a part of the secondstacked dielectric layer is disposed between the control gate electrodeand the insulating layer. In one or more foregoing or followingembodiments, no portion of the gate dielectric layer is disposed betweenthe first stacked dielectric layer and the control gate electrode.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor device comprising: an insulatinglayer disposed over a substrate; a semiconductor wire disposed over theinsulating layer; a first gate dielectric layer disposed around a firstpart of the semiconductor wire; a first gate electrode disposed on thefirst gate dielectric layer; and a first bottom dielectric layerdisposed between the first gate electrode and the insulating layer, andeach of the first gate dielectric layer and the first bottom dielectriclayer include three dielectric layers.
 2. The semiconductor device ofclaim 1, further comprising a side dielectric layer disposed on one sideface of the first gate electrode layer and includes three dielectriclayers.
 3. The semiconductor device of claim 2, wherein the sidedielectric layer including the three dielectric layer is not disposed onanother side face opposite to the one side face of the first gateelectrode.
 4. The semiconductor device of claim 2, wherein the firstgate dielectric layer, the first bottom dielectric layer and the sidedielectric layer are continuous.
 5. The semiconductor device of claim 2,further comprising: a second gate dielectric layer disposed around asecond part of the semiconductor wire; and a second gate electrodedisposed on the second gate dielectric layer, wherein the sidedielectric layer is disposed between the second gate electrode and thefirst gate electrode.
 6. The semiconductor device of claim 5, whereinthe second gate dielectric layer has a different film configuration thanthe first gate dielectric layer.
 7. The semiconductor device of claim 5,further comprising a second bottom dielectric layer disposed between thesecond gate electrode and the insulating layer, wherein the second gatedielectric layer and the second bottom dielectric layer are made of asame material.
 8. The semiconductor device of claim 5, wherein a heightof the first gate electrode is smaller than a height of the second gateelectrode.
 9. The semiconductor device of claim 1, wherein: the threedielectric layers includes a first layer made of oxide, a second layermade of one of SiN, SiON, HfO₂ and ZrO₂ and a third layer made of oxide.10. A semiconductor device, comprising: an insulating layer disposedover a substrate; a semiconductor wire disposed over the insulatinglayer; a first gate dielectric layer disposed around a first part of thesemiconductor wire; a first gate electrode disposed on the first gatedielectric layer; a second gate dielectric layer disposed around asecond part of the semiconductor wire; and a second gate electrodedisposed on the first gate dielectric layer, wherein the first gatedielectric layer is in contact with the second gate dielectric layer.11. The semiconductor device of claim 10, wherein the first gatedielectric layer extends between a side of the first gate electrode anda side of the second gate electrode.
 12. The semiconductor device ofclaim 11, wherein: the first gate dielectric layer includes a firstlayer disposed on the first part of the semiconductor wire, a secondlayer disposed on the first layer and a third layer disposed on thesecond layer, and the first layer extends beyond the first gateelectrode and wraps around a third part of the semiconductor wire. 13.The semiconductor device of claim 12, wherein the first layer isdisposed on a top face of the second gate electrode.
 14. Thesemiconductor device of claim 13, wherein the first layer is disposed ona side face of the second gate electrode and wraps around a fourth partof the semiconductor wire.
 15. A semiconductor device comprising: aninsulating layer disposed over a substrate; a semiconductor wiredisposed over the insulating layer; a first gate dielectric layerdisposed around a first part of the semiconductor wire; a first gateelectrode disposed on the first gate dielectric layer; and a protrusionprotruding from the substrate and disposed just below the semiconductorwire, wherein the first gate dielectric layer includes a first layermade of oxide, a second layer made of one of SiN, SiON, HfO₂ and ZrO₂and a third layer made of oxide.
 16. The semiconductor device of claim15, wherein the protrusion is embedded in the insulating layer.
 17. Thesemiconductor device of claim 16, further comprising: a second gatedielectric layer disposed around a second part of the semiconductorwire; and a second gate electrode disposed on the first gate dielectriclayer, wherein the first gate dielectric layer extends between a side ofthe first gate electrode and a side of the second gate electrode. 18.The semiconductor device of claim 17, wherein no portion of the secondgate dielectric layer is disposed between the first gate dielectriclayer and the first gate electrode.
 19. The semiconductor device ofclaim 17, wherein no portion of the first gate dielectric layer isdisposed between the second gate dielectric layer and the second gateelectrode.
 20. The semiconductor device of claim 17, wherein: a part ofthe first gate dielectric layer is disposed between the first gateelectrode and the insulating layer, and a part of the second gatedielectric layer is disposed between the second gate electrode and theinsulating layer.